1. Field of the Invention
The present invention relates to a communications apparatus with a number of terminal equipments connected to a network. More particularly, it relates to a control circuit for controlling terminal identifiers for identifying terminal equipments.
2. Description of the Prior Art
The apparatus performing communication processing according to the HDLC (High-level Data Link Control)-type data link layer controlling procedure has been known. FIG. 1 shows a configuration of an in-house network shown in the CCITT Recommendation I.430, and a subscriber line 41 such as a telephone line controls an in-house bus 42, and a controlling apparatus 43 terminating the subscriber line is connected thereto, and terminal equipments TE0, TE1 . . . TEn such as a telephone and a facsimile are connected to the in-house bus 42. Numerals 44, in the figure designate terminating registors.
In the above-mentioned Recommendation, one telephone number corresponds to one controlling apparatus 43, and discrimination of the terminal equipments TE0, TE1 . . . TEn is made using subaddresses called terminal equipment identifiers TEI. For this reason, the terminal equipments are to exchange signals for determining the TEI value with the network, prior to communication, to secure the TEI value thereof. When the communication is completed, the terminal equipments may release their TEI values.
The network, on the other hand, gives an unused TEI to the terminal equipment every time assignment of a TEI is requested by a terminal equipment. This TEI normally is not released even after the communication has been completed. According to the above recommendation, there are maximum 8 terminal equipments and maximum 128 TEI values. Since the network does not release a TEI value once used, after a communication has been completed, the TEI values to be assigned to a terminal equipment may run short after repeated communications.
In such a situation, the network starts the TEI check procedure to check if TEIs are being used or not, and releases an unused TEI value to provide for the next TEI assignment request.
So far, the above release process has been exercised by software, but the processing rate is small and there is a problem that a TEI assignment request just after the TEI value has run short cannot be answered. There is also another problem that the processing by software uses the bus in the system, resulting in restricting the data processing rate.